Electrodeposition of particulate coating material



Dec. s, 19,70

-W. W. PENDLETON Ef AL ELECTRODEPOSITION 0F PARTIGULATE COATING MATERIAL, r

Filed Nov. 7. 1967 United States Patent O M 3,546,017 ELECTRODEPOSITION OF PARTICULATE COATING MATERIAL Wesley W. Pendleton and William W. Ulmer, Muskegon,

Mich., assignors to Anaconda Wire and Cable Company, a corporation of Delaware Filed Nov. 7, 1967, Ser. No. 681,198 Int. Cl. H01b 3/00; B44d 1/094 U.S. Cl. 117-232 10 Claims ABSTRACT F THE DISCLOSURE Dielectric particles for electrostatic deposition are mixed with a small proportion of barium titanate or other high-dielectric-constant particles to increase the rate and efliciency of a coating process.

BACKGROUND OF THE INVENTION This invention relates to the coating of surfaces and particularly to the continuous coating of elongated conductors by electrostatic deposition. In application Ser. No. 588,511, now patent 3,396,699, an improvement is described in apparatus for electrostatically coating a continuous conductor passing through a cloud of particles above a fluid bed, and coating apparatus is commercially available in several varieties that operate on principles of electrostatics. In such apparatus an electrical potential, usually in the range of 30,000-l00,0\00 volts, is impressed between the object to be coated and an electrode spaced from the object. The coating particles are introduced between the electrode and the object and may become charged either by contact with the electrode, other charged particles, or the ionized air.

In the commercial use of electrostatic coating methods, including the practice of xerographic printing, it is,

of course, desirable to apply a given thickness of coating in as short a time as possible. The rate of application increases with an increased potential difference but a higher potential requires greater spacing of the electrode from the object being coated, and, where the particles are charged by contact with the electrode, a higher potential will then mean that the particles must travel a longer path.

It is not always possible to place the article being coated symmetrically with respect the electrode and it has been considered an advantage of the electrostatic method of coating that the particles will deposit around corners onto surfaces that are not in direct line with the particle supply source. This is particularly true in the case where a moving wire or strip is being coated in a cloud of particles above a fluid bed. In the commercial application of this method, however, the far surfaces have not always been uniformly coated when speeds were increased to those speeds wherein the near surfaces received a sufficient coating.

We seek therefore by our invention to obtain electrostatic depositions in shorter times.

We seek further, by our invention, to obtain coatings at lower potentials.

We seek, further, by our invention, to obtain more uniform electrostatically deposited coatings.

SUMMARY In a process for coating a surface by means of electrostatically charged particles, particularly particles having a dielectric constant under 10, we have invented the irnprovement of mixing among these particles a small percentage of a, preferably much iiner, particulate material, such, by preference, as barium titanate, having a dielectric constant, at the temperature of deposition, of at 3,546,017 Patented Dec. 8, 1970 least 1500. Our invention has particular application to the deposition of an organic resin, such as one comprising an epoxy, upon a continuously advancing conductor, such as a wire, and the subsequent fusing of the resin on the conductor.

Our invention comprises also the powdered mixture, for deposition, of particles of a coating material, and a small weight percentage of a substance, such as barium titanate, with a dielectric constant in excess of 1500. The barium titanate or other high-dielectric-constant substance is preferably substantially finer than the coating material. In certain preferred embodiments the coating material of our mixture comprises an organic resin such as an epoxy.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 represents a container of the mixture of our invention with the particle sizes very much enlarged.

FIG. 2 shows a scheme of the process of our invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. l a mixture, indicated generally by the numeral 10, has been prepared for coating the surface of an object such as an electrical Wire strip that is passed continuously adjacent to an electrostatically charged supply of said particles. This mixture comprises a large plurality of particles 11 of an epoxy resin of a type known for electrical insulation coating or the constituents of such a resin.

A suitable epoxy resin comprises about 77.31 parts of Epi Rez #530 C, f9.59 parts Epi Rez #540, .23 part of hexarnethylene tetramine, 10.5 parts of trimellitic anhydride and .87 part of powdered silica (Cab-o-Sil, supplied by Godfrey L. Cabot, Inc.). Epi Rez is supplied by the Celanese Plastics Company. Although we have described a mixture where the particles 11 comprise epoxy, other resins suitable for electrodeposition may be used, of which polyolens, polyesters, polyacrylics, polyvinyls, polyamids, polyimids are listed by way of example. The dielectric constant of these materials is preferably lower than 4 and invariably lower than 10. Inorganic glasses and ceramics or blends thereof, that will be fused on a coated object can also comprise the particles 11 within the scope of our invention as can pigment particles which are known for use in the practice of xerography.

In the preferred example the epoxy particles 11 had the following mesh analyses-on mesh, 9.2%; on 200 mesh, 28.9%; on 230 mesh, 23.6%; on 270 mesh, 13.4%; on 325 mesh, 13.2%; on 400 mesh, 6.7%; through 400 mesh, 5%. Generally we favor a particle size for the coating material from .5-3.5 mils in diameter.

Interspersed uniformly among the particles 11 are particles 12 of barium titanate to the amount of about 1% of the Weight of the particles 11. Barium titanate has a dielectric constant at room temperature of 1740 and a low dissipation factor (0.63%) which is advantageous in an electrical insulation. We prefer that the particle size of the barium titanate should be much iiner than the size of the particles 11 and all of it is passed through 400 mesh. Consequently, although the weight of the barium titanate added is relatively small the number of particles in the blend are sufficient to effect its behavior in an electric eld. It is preferred to have the high-dielectric-constant powder in a particle size from .01 to .05 mil. We prefer that the BaTiO3 be from 0.5-1.5% of the Weight of the particles 11 but weights from .1 to 5% may be used with advantageous effect depending on the relative particle sizes and selection of high-dielectric-constant material.

Other high-dielectric-constant materials that can be used in the practice of our invention include combinations of barium titanate and strontium titanate of which the compound with a barium:strontium ratio of 79:21 has a dielectric constant of 8700, that with a barium:strontium ratio of 71:29 has a dielectric constant of 2990 and that with a barium:strontium ratio of 90:10 has a dielectric constant of 1310. The dissipation factor of the 79:21 barium strontium compound is high, 2.30%, but, because the quantity of the compound that will finally be fused into the insulation is low, the high dissipation factor will not be objectionable for many electrical insulation applications, and of course, will be no hindrance at all for nonelectrical coatings. Ferrites are known with dielectric constants as high as 680,000 and these too are useful in the practice of our invention although their cost, at present, is high for many commercial applications.

It is noteworthy, however, that when TiO2, which has a dielectric constant of 100, was employed in the same manner as the BaTiO3 to improve powder deposition no improvement was observed.

In FIG. 2, in a preferred method of our invention, a reel of rectangular magnet wire conductor 13, grounded at 14 is continuously advanced through a cloud 16 of electrostatically charged particles maintained by known methods around the conductor. A suitable method employs a uid bed as hereinabove cited. A high potential is maintained on a plate 17 by means of a transformerrectifier 18 or other suitable means in a known manner. Instead of the plate 17 the high potential might be applied to the nozzle of a powder spray unit of which several types are commercially available. The cloud 16 is supplied from a mixer 19 which may also advantageously comprise a pulverizer, into which are paid the coating particles 21 CTI ' prise barium titanate.

3. The process of claim 1 wherein said heat fusible particles comprise an organic resin.

4. The process of claim 2 wherein said heat fusible particles comprise an organic resin.

5. The process of claim 1 wherein said particles are substantially finer in size than said powder.

6. The process of claim 2 wherein said barium titanate is substantially finer in size than said powder.

7. The process of insulating a conductor comprising the i steps of:

and a small proportion of high-dielectric-constant particles 22. In an oven 23 the coating is fused on the conductor which is then cooled and taken up on a reel 24.

When an epoxy resin was deposited on a copper strand passing through an electritied particle cloud at the rate of 30 ft./min. with an electrostatic potential of 100 kv., the wall thickness of insulation deposited was 2.0 to 2.4 mils. When .79% of barium titanate was added to an essentially similar epoxy powder the same rate of deposition was obtained at only 50 kv. potential and at 100 kv. the deposition was 4-5 mils. (In this experiment .21% of strontium titanate was also added but since the dielectric constant of this material is only 234 the barium titanate accounts for the improved deposition). When 2.5% of barium titanate was included (with no strontium titanate) a deposition of 6-7 mils was obtained at only 85 kv. at 36 ft./min.

We have invented a new and useful process and product of which the above description has been exemplary rather than definitive and for which we desire an award of Letters Patent.

We claim:

1. The process of coating an electrically conducting surface comprising the steps of:

(A) blending a mixture of electrostatically chargeable,

(A) applying a high electric potential between said conductor and an electrode spaced therefrom,

(B) blending a mixture of particles of a dielectric organic resin and 0.1% to 5% of the weight of said particles of particles of a material having a dielectric constant of at least 1500.

(C) introducing said mixture between said conductor and said electrode thereby depositing said particles of resin and said material upon said conductor, and

(D) fusing said resin particles upon the surface of said conductor.

8. The process of claim 7 wherein said conductor comprises a continuously advancing wire.

9. The process of claim 7 wherein said material comprises barium titanate.

10. The process of claim 7 wherein said resin comprises an epoxy.

References Cited UNITED STATES PATENTS 2,919,247 12/1959 Allen 252-621 3,203,821 8/1965 Domin' 117-17 3,239,465 3/1966 Rheinfrank 117-17.5 3,342,621 9/1967 Point et al. 117-17 FOREIGN PATENTS 3,563,663 12/1961 Japan 117-17 WILLIAM D. MARTIN, Primary Examiner 5 R. M. SPEER, Assistant Examiner U.S. C1. X.R. 117-17, 21, 224

go UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,546J 017 4 Dated 12/8/70 Inventods) Wesley W. Pendleton and William W. Ulmer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

rColumn l, line 47, after "respect" insert to.

Column 2, line 64, for "effect" read affect.

Claim 7, column 4 line 30, after 1500 change the period to '3. Coma was ma :32,1121:v B230 NI Anm:

mwN-Wh mm1. m nesting Offiwll'l dominican of Patent 

